1. Field of the Invention
Aspects of the present invention relate to a method to share resources using Cognitive Radio (CR) technology in a wireless network and, in particular, to an explicit outband signaling method to detect sharable resources for management of public resources.
2. Description of the Related Art
Recently, various types of wireless communication technologies have been developed and wireless communication technologies are being commonly used in daily life. The development of wireless communication technologies aims at providing data communication services, rather than voice-oriented services, at higher speed and lower cost. Therefore, an increase in the required amount of wireless resources is inevitable. The wireless resources can be frequency bands. However, most available wireless resources have already been allocated for existing wireless networks or existing communication services. For this reason, it is not possible to fulfill the demand for wireless resources, which is increasing due to the advent of new wireless networks and new communication services.
Cognitive Radio (CR) technology has been proposed as a scheme to use limited wireless resources efficiently. The CR technology allows another wireless network to share unused wireless resources among the wireless resources allocated to a particular wireless network. The need for the CR technology is increasing due to the present lack of wireless resources.
FIG. 1 illustrates an example of a general wireless network using CR technology. A first base station (BS) 110 is part of an existing wireless network that has already been allocated required wireless resources. The first base station 110 provides communication services for first user equipment 112, 114, 116, and 118 with the allocated wireless resources. A second base station 120 is part of a new wireless network that has been allocated no wireless resource, or has not been allocated sufficient wireless resources. The second base station 120 shares the wireless resources of the first base station 110 using the CR technology and provides communication services for the second user equipment 122, 124, 126, and 128 with public wireless resources.
The first base station 110 and the second base station 120 each have their own unique service areas where they will provide communication services. The first user equipment 112, 114, 116, and 118 are located in the service area of the first base station 110 and the second user equipment 122, 124, 126, and 128 are located in the service area of the second base station 120.
In addition, there is an area (hereinafter referred to as an “interference area”) where the service area of the first base station 110 and the service area of the second base station 120 overlap. If the first base station 110 and the second base station 120 do not use the same wireless resources (i.e., the same channels), the user equipment may not experience interference with other base station signals even though they are located in the interference area. However, if the first base station 110 and the second base station 120 use the same wireless resources (i.e., the same channels), the user equipment located in the interference area may experience interference with other base station signals.
For example, assume that the second base station 120 provides communication services for the second user equipment 128 located in the interference area, using a channel x. The channel x corresponds to a wireless resource allocated to the first base station 110 but is not actually used. Assume that in this situation, the first base station 110 starts a communication service for at least one of the first user equipment 112, 114, 116, and 118 using the channel x. In this case, a signal transmitted from the first base station 110 and a signal transmitted from the second base station 120 are received together at the second user equipment 128 through the channel x. Therefore, the second user equipment 128 cannot decode the signal transmitted from the second base station 120 through the channel x, making communication impossible.
However, because the second base station 120 is not in the service area of the first base station 110, it cannot recognize the fact that the channel x is used by the first base station 110. Therefore, the second base station 120 will continue to transmit signals using the channel x. The signals continuously transmitted from the second base station 120 through the channel x serve as interference signals for the first user equipments 112 and 114 located in the interference area.
In order to solve the problem occurring by applying the CR technology to the conventional wireless network, there is a need for a scheme in which a second base station can recognize the fact that the channel x is used by the first base station.